I do remember seeing pics of the PCE CD prototype before the PCE console was released, so obviously it wasn't an after thought. Funny, internally the PCE was referred to as the 'Core' system and then later on the name was changed to that. Another interesting note; the PCE is the mother of all addon interfaces. What's available on the back plane - it just incredible. No other game console in history had that type of addon support. It was built for addons. It's a shame they didn't do more with it.
It may be true that there is more available through the back connection than most any other addon port, but many systems certainly are designed for addons, and lots of them have gotten addons. I mean, sure, it holds back the Sega CD a bit that the port bandwidth is a bit too limited for animation equal to that on carts, but it gets by... and it was designed for an addon like that, they just didn't quite give it enough bandwidth. But that doesn't mean it wasn't designed for addons from the start, it was! The same goes for all the other systems with addon ports and the like.
But sure, yeah, the system clearly was designed for addons from the beginning. We know that Hudson got interested in CDs early on, and NEC was a good partner since they were too...
Hudson might have licensed the hardware setup to NEC, but they partnered together. Hudson has always been a software house and has written internal dev tools for Famicom, Sharp X68k, etc. Hudson was NEC's software side, until NEC started creating its own branch. And even then..
Well, yeah, at first only Hudson did software, but NEC Avenue started publishing its own games by fall '88, and NEC Avenue and Hudson were different companies. It's definitely a somewhat weird situation, with multiple first-party companies, but that's how it was. Just about the only other somewhat similar case I can think of is the 3DO, where at first there was no first party studio. 3DO set up one after a little while though, and Panasonic published many games for the system though they didn't develop them in-house (Goldstar/LG and Sanyo published a couple of games each as well). But another case with multiple different first-party studios with in-house development teams? Are there any others other than the TG16?
I'm sure NEC and Hudson cooperated, they were working together on the console after all, but they weren't the same exact company.
It's funny, the NEC had a close tie with x86 arch as well as making its own clone x86 processors. The official dev softs for the CD unit, refers to internal Zeropage reserved registers (65x thing) with x86 register names; AX(AL/AH), BX(BL/BH), CX(CL/CH), DX(DL/DH), SI, DI, etc. The MCU in the CD unit, is a NEC z80 based processor (this is the chip that manages the port interfacing and requesting status info as well as writing SCSI commands). NEC also released the CD unit for its PC line, which is compatible and fits the original docking bay of the PCE. NEC tasked Hudson with designing the CD unit (it was in some interview). I think it's pretty hard to separate NEC and Hudson, when talking about the PCE. Hudson might have developed the original specs for the PCE, but who knows how much that changed when they partnered with NEC (the GPU can be put into 2bit color tile/cell mode for both sprites/BG).
Interesting, so NEC actually did have some influence on the hardware? I thought Hudson had pretty much done the hardware in-house... interesting. I have heard of the computer you could attach a TCD drive to, though. They were going to release something similar in the US too of course, but cancelled it...
Anyway though, it may be hard to separate NEFC and Hudson, but they're not the same. They started at different times ((Hudson ~10 months ahead of NEC on both HuCards and CDs), they ended at different times (NEC continued to publish TCD games regularly for ~16 months after Hudson abandoned the system, while Hudson released many more HuCard games in '92-'93 than NEC, who had almost entirely abandoned HuCards in favor of CDs), etc. Hudson also continued to support other, mostly Nintendo platforms throughout the TG16/CD/PCFX's lives of course, at first just the NES and SNES but also the SNES starting from late '92, and the Saturn starting in '96 as well. Except for that last part NEC did not do that; they were Turbo-line exclusive until mid '96, when they admitted that the PC-FX was failing and started supporting the Saturn too. That both went to the Saturn first after the PC-FX in the 5th generation is similar, and interesting considering how few Genesis and Sega CD games Hudson had made (and were any of them even released in Japan? As far as I know they were all US/EU only -- Mega Bomberman, SCD Dungeon Explorer, SCD Lords of Thunder, SCD Cobra 2...), but that was during the Saturn's peak of popularity in Japan, so it's understandable either way.
Anyway, yes, I'm sure that Hudson and NEC worked together a lot, cooridinated, etc. But they were never exactly the same company, and each did their own things. Their libraries on the TG16/CD have some definite differences, for example... Hudson's games often have a strong unique style which you don't see from NEC.